1. Field of the Invention
The present invention generally relates to a satellite capturing/tracking method, and a satellite capturing/tracking apparatus. More specifically, the present invention is directed to satellite capturing/tracking method and apparatus used to mutually capture/track a space station and a data relay satellite while a data communication is carried out via the data relay satellite between the space station and an earth station.
2. Description of the Related Art
Conventionally, as a method for capturing and/or tracking a data relay station by a space station, such a tacking method has been utilized by combining an RF automatic tracking method with a program tracking method. First, in this RF automatic tracking method, the antenna is driven in such a way that the main axis of the antenna employed in the space station is directed to the transmission (propagation) direction of the electromagnetic waves. After the electromagnetic waves have been captured with the capture range of the antenna, this RF automatic tracking method can be actuated. To capture the electromagnetic waves within the capture range of this antenna, the program tracking method is employed in order that the antenna is directed to the transmission direction of the electromagnetic waves. In this program tracking method, a data relay satellite is tracked by a space station as follows. An earth station determines an orbit of the space station and an orbit of the data relay satellite, and then calculates a capturing/tracking parameter based upon the determined orbits. The resultant capturing/tracking parameter is registered, or programmed in both the data relay satellite and the space station.
In the above-described conventional satellite capturing/tracking method, since this capturing/tracking method depends upon the orbit decisions made by the earth station, the space station must capture/track the data relay satellite even in such a case that both the data relay station and the space station are located within the invisible range with respect to the earth station. As an operation method for such a capturing/tracking method, Japanese Unexamined Patent Application No. 7-10096 discloses the below-mentioned operation technique. First, when the data relay satellite is located within the visible range, the earth station transmits both the microcommand and the data table to the data relay satellite. The microcommand is produced by symbolizing a series of operation sequences as a single command having a command issuing time instant. The data table is employed so as to expand this microcommand into a series of base command groups used to actually operate the satellite. As a result, the data relay satellite expands the received microcommand to the base command group with reference to the received data table. The command issuing time instant which is described at the satellite time is added to this base command group. Thereafter, when the space station is entered into the visible range, the earth station transmits the base command related to the space station among this expanded base command group to the space station.
On the other hand, the data relay satellite and the space station receive electromagnetic waves sent from 4 sets of GPS (Global Positioning System) satellites so as to make both the satellite time instants coincident with the GPS time corresponding to the absolute time instants defined in the GPS system.
As a result, the data relay satellite and the space station compare the respective satellite time instants with the command issuing time instants added to the respective base commands. When these time instants are made coincident with each other, the data relay satellite and the space station issue this command to the respective electronic appliances employed in the own satellite and the own space station, so that the data relay satellite and space station can be automatically operated without being instructed by the commands transmitted from the earth station.
On the other hand, in the above-described conventional satellite capturing/tracking method, since the orbits of the space station and the data relay satellite are determined, depending upon the earth station, there is such a drawback that this may give adverse influences to the operation loads of the earth station.
Also, in the conventional capturing/tracking method described in Japanese Unexamined Patent Application No. 7-10096, since it is a fact that the same time instant never appears twice, the capturing/tracking parameter must be periodically calculated and registered, or programmed by the earth station. Therefore, this causes another problem that the operation loads given to the earth station are similarly adversely influenced.